Matt Allen must play a waiting game before discovering whether he will face his former club Northampton in tomorrow night's Heineken Cup opener at Cardiff Arms Park.

Matt Allen must play a waiting game before discovering whether he will face his former club Northampton in tomorrow night's Heineken Cup opener at Cardiff Arms Park.

The ex-Saints centre is on standby for a midfield place as Cardiff's South African centre Pieter Muller struggles to shake off a calf strain.

England A cap Allen, a member of Northampton's Heineken Cup final-winning team last year, quit Saints during the summer and moved west.

"If Pieter is not 100% fit, then Matt will start," said Cardiff coach Rudy Joubert.

"Matt is a key man for us, and I am sure that he will prove he was a big loss to Northampton if he plays on Friday night."

Cardiff, cup quarter-finalists in each of the past two seasons, include recent back-row signings Francois Mounier and Semo Sititi among their starting XV, while Lions Rob Howley and David Young also feature.

Andy Nicol's team currently lead the Welsh-Scottish League, and include all nine of their players on Six Nations Championship duty for Scotland against Ireland last Saturday.

Andrew Henderson, a try-scoring substitute at Murrayfield, partners James McLaren in midfield, while the pack features Lions hooker Gordon Bulloch and talented back-five forward Jason White.

Leinster will field 11 internationals when they take on French champions and pool six favourites Toulouse tomorrow.

Lions centre Brian O'Driscoll has been given the green light following an injury scare during Ireland's 32-10 defeat in Edinburgh, with coach Matt Williams looking to build on a Celtic League campaign that has so far seen Leinster record seven successive wins.

The game has been switched from Toulouse after a chemical factory explosion killed 29 people there last week, and a minute's silence in memory of the victims will be observed.